RGS (Regulators of G protein Signaling) proteins modulate the information transduced into cells through G protein signaling pathways. Approximately thirty RGSs have been identified. All of these proteins contain a highly conserved RGS domain, but differ in the presence of additional protein-protein interaction motifs that are thought to specify interactions with signaling partners. The presence and arrangement of these motifs defines several distinct families of RGS proteins. RGS9-2 is a brain-specific member of a group of RGS proteins identifiable by the tandem arrangement of 4 protein- protein interaction domains, namely a Dishevelled egllO, pjeckstrin (DEP) domain, a G-gamma-like (GGL) domain, a Regulator of G protein signaling (RGS) domain, and a C-terminal proline-rich domain. This protein exhibits a remarkable distribution in the central nervous system, with very high levels of expression only in the striatum, and during development, also in the cerebral cortex. This distribution suggests a role for RGS9-2 in regulating specific aspects of G protein signaling in these regions, and hence a potential role in the pathophysiology of neuropsychiatric disorders. In fact, RGS9-2 has been shown to be increased in Parkinson's disease and to facilitate tolerance to opioids. Unfortunately, little is known at the present time about the specific function(s) of the RGS9-2 in the brain. In an effort to understand the role of RGS9-2 at a cellular/molecular level, our laboratory has focused on the identification of specific signaling partners for this protein. Using yeast two hybrid screen and co- immunoprecipitation techniques, we have identified a strong interaction between RGS9-2 and a-actinin-2. One of the best understood roles for a-actinin-2 is in the regulation of NMD A receptor desensitization. Consistent with a physiological role for the interaction between RGS9-2 and a-actinin-2, in preliminary studies we have uncovered a strong regulation of NMD A currents by RGS9-2. Combined, these results suggest a novel and potentially very exciting role for RGS9-2 in central forebrain neurons. In the present application, we propose to extend these preliminary observations by addressing these three questions: 1) what specific regions within RGS9-2 and a-actinin-2 are critical for their mutual interaction, 2) do RGS9-2 and a-actinin-2 colocalize in the brain, 3) does the interaction between RGS9-2 and a-actinin-2 have functional significance for NMDA receptor function. To answer these questions, we propose the following aims: Specific Aim 1. To identify the regions most critical in mediating the interaction ofRGS9-2 and a-actinin-2, and to determine the functional relevance of this interaction. Specific Aim 2. To assess the physical and functional interaction between RGS9-2 and a-actinin-2 in central neurons. [unreadable] [unreadable] [unreadable]